MEMS/NEMS and BioMEMS/BioNEMS Materials and Devices · PDF fileMEMS/NEMS and BioMEMS/BioNEMS...

MEMS/NEMS and BioMEMS/BioNEMS Materials and Devices and Biomimetics

Prof. Bharat BhushanOhio Eminent Scholar and Howard D. Winbigler Professor

d Di t NLBBand Director [email protected]

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics

© B. BhushanNanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics

Micro/nanoscale studies

Bio/nanotribology Bio/nanomechanics Biomimetics

Materials sci biomedical eng physics & physical chem

Materials/DeviceStudies

• Materials/coatings

Techniques

Materials sci., biomedical eng., physics & physical chem.

NanoindentorMicrotriboapparatusAFM/STM

• SAM/PFPE/Ionic liquids• Biomolecular films

• CNTs

• Micro/nanofabricationNanoindentorMicrotriboapparatusAFM/STM

Collaborations Applications

Numerical modeling and simulation

Collaborations

• MEMS/NEMS• BioMEMS/NEMS• Superhydrophobic surfaces• Reversible adhesion

Applications

• Beauty care products• Probe-based data storage• Aging Mech. of Li-Ion Batt.



3

Outline• Background

Definition of MEMS/NEMS and characteristic dimensionsExamples of MEMS/NEMS and BioMEMS/bioNEMS with nanotribology and nanomechanics issuesBiomimetics – Lessons from Nature

• ExperimentalExperimentalAtomic force/Friction force microscope (AFM/FFM)

• Tribological Studies of Si and Related MaterialsVirgin, treated/coated silicon; polysilicon films and SiC film

• Tribological Studies of LubricantsPerfluoropolyether lubricants and self-assembled monolayers

• Bioadhesion StudiesSurface modification approaches to improve bioadhesionpp p

• Device Level StudiesAdhesion, friction and wear measurements using a microtriboapparatusNanotribological characterization of digital micromirror devices (DMD)

• Hierarchical Nanostructures for Superhydrophobicity, self cleaning and low adhesion (Lotus Effect)Roughness optimization for superhydrophobic and self cleaning surfacesExperimental studies

• Hierarchical Nanostructures for Reversible Adhesion (Gecko Feet)


Hierarchical structure for adhesion enhancementRoughness optimization for reversible dry adhesives (not included)

BackgroundDefinition of MEMS/NEMS and characteristic dimensions

Human hair50-100 μm

MEMS - characteristic length less than 1 mm,larger than 100 nm

NEMS - less than 100 nm

50 100 μm

DMD12 μm

500 nm

Molecular gear10 nm-100 nm

Red blood cell8 μm

Quantum-dots transistor300 nm

10 nm 100 nm

SWNT chemical sensor2 nm

0.1 1 10 100 1000 10000 100000

C atom0.16 nm

DNA2.5 nm

Characteristic dimensions in perspectiveB. Bhushan, Springer Handbook of Nanotechnology, Springer, 2nd ed. (2007)

Size (nm)


Stiction – High static friction force required to initiate sliding. Primary source is liquid mediated adhesion

Formation of meniscus and contribution to the attractive force


B. Bhushan, Introduction to Tribology, Wiley, 2002

Examples of MEMS/NEMS and BioMEMS/NEMSp

shuttle

springs

Microgear unit can be driven at speeds up to 250,000 RPM. Various sliding comp. are shown after wear test for 600k cycles atshown after wear test for 600k cycles at 1.8% RH (Tanner et al., 2000)

gears and pin joint


Microengine driven by electrostatically-actuatedcomb drive

Sandia Summit Technologies (www.mems.sandia.gov)Stuck comb drive


Microfabricated commercial MEMS components

8

The generating points of friction and wear due to interaction of a biomolecular layer on a synthetic microdevice with tissue

(Bhushan, Lee et al., 2006)


9

Need to address nanotribology and nanomechanics issues• The nanotribology and nanomechanics problems can drastically

compromise device performance and reliability. To solve these problems, there is a need to develop a fundamental understandingof adhesion friction/stiction wear and the role of surface

gy

of adhesion, friction/stiction, wear and the role of surface contamination and environment in MEMS/NEMS and BioMEMS/NEMS. This can be done by studying

Nanotribology and nanomechanics of MEMS/NEMS materialsNanotribology and nanomechanics of MEMS/NEMS materialsLubricant methods for MEMS/NEMSBioadhesion StudiesDevelopment of superhydrophobic surfacesDevice level studies

Approach• Use an AFM/FFM for imaging and to study adhesion friction scratch andUse an AFM/FFM for imaging and to study adhesion, friction, scratch and

wear properties of materials and lubricants, which better simulates MEMS/NEMS and BioMEMS/BioNEMS contacts

• Develop and employ techniques to measure tribological phenomena in


B. Bhushan et al., Nature 374, 607 (1995); B. Bhushan, Handbook of Micro/Nanotribology, second ed., CRC Press, 1999;B. Bhushan, Introduction to Tribology, Wiley, NY, 2002; B. Bhushan, Springer Handbook of Nanotechnology, 2nd ed., 2007;B. Bhushan, Nanotribology and Nanomechanics – An Introduction, Springer, 2005.

devices

Biomimetics

Lessons From Nature (Biomimetics)Biomimetics• Nature has gone through evolution over 3.8 billion years. It has evolved

objects with high performance using commonly found materials.Biomimetics means mimicking biolog or nat re It is deri ed from a• Biomimetics means mimicking biology or nature. It is derived from a Greek word “biomimesis.” Other words used include bionics, biomimicry and biognosis.Biomimetics involves taking ideas from nature and implementing them in• Biomimetics involves taking ideas from nature and implementing them in an application.

• Biological materials have hierarchical structure, made of commonly found materialsfound materials.

• It is estimated that the 100 largest biomimetic products had generated $1 200 08$1.5 billion over 2005-08. The annual sales are expected to continue to increase dramatically.


11M. Nosonovsky and B. Bhushan (2008), Multiscale Dissipative Mechanisms and Hierarchical Surfaces: Friction, Superhydrophobicity, and Biomimetics, Springer-Verlag, Heidelberg, Germany; B. Bhushan (2007), Springer Handbook of Nanotechnology, second ed., Springer-Verlag, Heidelberg, Germany; B. Bhushan, Phil. Trans. R. Soc. A 367, 1445-1486 (2009).

Overview

Overview of various objects from nature and their selected

f tifunction

12

Nanoprobe Laboratory for Bio- & Nanotechnology and BiomimeticsB. Bhushan, Phil. Trans. R. Soc. A 367, 1445-1486 (2009).

Montage of some examples from nature.


13B. Bhushan, Phil. Trans. R. Soc. A 367, 1445-1486 (2009).).

Atomic force/Friction force microscope (AFM/FFM)Experimental

p ( )• At most interfaces of technological relevance, contact occurs at

numerous asperities. It is of importance to investigate a single asperity contact in the fundamental tribological studies.

Tip - based microscope allows simulation of a single asperity contact

Engineering Interface

• Nanotribological studies are neededTo develop fundamental understanding of interfacial phenomena on a small scale

simulation of a single asperity contact

on a small scaleTo study interfacial phenomena in micro- or nanostructures and performance of ultra-thin films used in MEMS/NEMS components


p


Large sample AFM/FFM

Three-sided pyramidalSquare pyramidal Square pyramidal Three-sided pyramidal (natural) diamond tip

Square pyramidal silicon nitride tip

Square pyramidal Single-crystal silicon tip

Carbon nanotube tip


Various AFM tips

Macroscale friction and wear performance of silicon Tribological Studies of Si and Related Materials

and effect of ion implantation

Reciprocating sliding tests against an alumina ball at 1 N load.V refers to virgin silicon. S and P correspond to doped single-crystal

and polycrystalline silicon. Ion energy used was 200 keV.


B. K. Gupta, B. Bhushan et al., ASME J. Tribol. 115, 392 (1993); B. K. Gupta, B. Bhushan et al., Tribol. Trans. 37, 601 (1994)

Scratch, wear and nanoindentation of virgin gand treated/coated silicon

Microscale scratch tests using a diamond tip in an AFMg p


B. Bhushan and V. N. Koinkar, J. Appl. Phys. 75, 5741 (1994)

Friction, scratch, wear and nanoindentation of polysilicon films and SiC film• Polysilicon films, undoped and doped are commonly used as

MEMS materials

• Silicon-based MEMS devices lack high-temperature capabilities with respect to both mechanical and electrical properties

• SiC is being pursued as a material for high-temperature microsensor and microactuator applications based on its successful use in high-power devices

SampleDensity(kg/m3)

Hardness(GPa)

Elastic modulus

(GPa)

Fracture toughness(MPa m1/2)

Thermal conductivity

(W/m K)

Coeff. of thermal

expansion(x 10-6 / οC)

Melting point(οC)

Band-gap(eV)

successful use in high power devices

(x 10-6 / οC)

β-SiC 3210 23.5-26.5 440 4.6 85-260 4.5 - 6 2830 2.3

Si(100) 2330 9-10 130 0.95 155 2 – 4.5 1410 1.1


Selected bulk properties of 3C SiC and Si(100)

AFM 3D maps and average 2D profiles of scratch marks on various samples


B. Bhushan, Tribology Issues and Opportunities in MEMS, Kluwer, 1998; S. Sundararajan and B. Bhushan, Wear 217, 251 (1998)

Summary of tribological studies of MEMS/NEMS materialsSummary of tribological studies of MEMS/NEMS materials

• Tribological properties of silicon are inadequate• Tribological properties of silicon are inadequate

• Ion implantation and oxidation of silicon improve the tribological properties of silicontribological properties of silicon

• SiC exhibits significantly better tribological properties than silicon-based materials and is a good candidate forsilicon-based materials and is a good candidate for MEMS/NEMS devices


Tribological Studies of Lubricants

• Chemically bonded liquid and solid lubricants with monolayer thicknesses are desired for low friction andmonolayer thicknesses are desired for low friction and wear.

• Lubricants must be hydrophobic to minimize effect of• Lubricants must be hydrophobic to minimize effect of environment.

Perfluoropolyether (PFPE) lubricantsPerfluoropolyether (PFPE) lubricantsSelf-assembled monolayers (SAMs)


Perfluoropolyether lubricantsp y

Z-15: CF3-O-(CF2-CF2-O)m-(CF2-O)n-CF3

Z-DOL: OH-CH2-CF2-O-(CF2-CF2-O)m-2 2 ( 2 2 )m(CF2-O)n-CF2-CH2-OH

•During cycling tests, the friction Z-DOL g y g ,(BW) exhibits the lowest friction and Z-15 shows negative effect.

•During cycling tests, the friction of g y g ,Si(100) and Z-DOL (BW) does not change. The friction of Z-15 film initially increases and reaches to a higher and stable value. The initial rise occurs because of the molecular interaction between the attached Z-15 molecules to the tip and the Z-15 molecules on the film surface.


Durability dataV. N. Koinkar and B. Bhushan, J. Appl. Phys. 79, 8071 (1996); J. Vac. Sci. Technol. A, 14, 2378 (1996);H. Liu and B. Bhushan, Ultramicroscopy 97, 321 (2003)

Self-assembled monolayers (SAMs)y ( )

P fl lk l il d lk l il SAM d it d Si(111) ithPerfluoroalkylsilane and alkylsilane SAMs were deposited on Si(111) with natural oxide and perfluoroalkylphosphonate and alkylphosphonate on Al.


B. Bhushan et al., Langmuir, 11, 3189 (1995); H. Liu, B. Bhushan, W. Eck and V. Stadler, J. Vac. Sci. Technol. A 19, 1234 (2001); B. Bhushan and H. Liu, Phys. Rev. B 63, 255412 (2001); B. Bhushan et al., Ultramicroscopy 105, 176 (2005); T. Kasai, B. Bhushan et al., J. Vac. Sci. Technol. B 23, 905 (2005); N. S. Tambe and B. Bhushan, Nanotechnology 16, 1549 (2005); Z. Tao and B. Bhushan, Langmuir 21, 2391 (2005); B. Bhushan et al., Microsyst. Technol. 12, 588 (2006); B. Bhushan and M. Cichomski, J. Vac. Sci. Technol. A 25, 1285 (2007); E. Hoque et al., J. Chem. Phys. 124,174710 (2006); J. Phys. Chem. B 110, 10855 (2006); J. Phys. Chem. C 111, 3956 (2007); J. Chem. Phys. 126, 114706 (2007); Ultramicroscopy (in press); DeRose et al., Surface Sci. 602, 1360 (2008) ;

PFTS showed lower adhesive force than and comparable coefficient of friction to ODMS and ODDMS.


Chain length has little effect. DP and ODP showed higher coefficient of friction and comparable adhesive force to ODMS and ODDMS.

AFM Microwear


A critical normal load was observed for SAMs, higher than that for substrates. Critical loads are lowest for ODMS and DP, moderate for PFTS, PFTP and ODP, and highest for ODDMS.

Bioadhesion Studies

• Study surface modification approaches - nanopatterning and y pp p gchemical linker method to improve adhesion of biomolecules on silicon based surfaces.


B. Bhushan et al., Acta Biomaterialia 1, 327 (2005) ; ibid 2, 39 (2006); S. C. Lee et al., J. Vac. Sci. Technol. B 23, 1856 (2005) ; D. Tokachichu and B. Bhushan, IEEE Trans. Nanotech. 5, 228 (2006); E. Eteshola et al., J. Royal Soc. Interf. 5, 123 (2008); B. Bhushan et al., J. Royal Soc. Interf. 5(in press)

Sample preparationSample preparation

STA: StreptavidinAPTES:AminopropyltriethoxysilaneNHS: N hydroxysuccinimidoNHS: N-hydroxysuccinimidoBSA: Bovine serum albumin


Schematic representation of deposition of streptavidin (STA) by chemical


linker method

Adhesion measurements in PBS with functionalized tipsp

Patterned silica surface exhibits higher adhesion compared to


Patterned silica surface exhibits higher adhesion compared to unpatterned silica surface. Biotin coated surface exhibits even higher

adhesion.

Microtriboapparatus for adhesion and friction Device Level Studies

measurements between MEMS components


H. Liu and B. Bhushan, J. Vac. Sci. Technol. A 21, 1528 (2003); B. Bhushan and Z. Burton, Nanotechnology 16, 467 (2005)

Adh i f t bi t diti


Adhesive force at ambient conditions

Device level studies - digital micromirror devices (DMD)e ce e e stud es d g ta c o o de ces ( )


AFM images of the arrays which wereremoved by ultrasonic method

Surface height

The stuck mirror can be identified and removed by AFM.

“Hard” stuck micromirror


Hard stuck micromirror

H. Liu and B. Bhushan, Ultramicroscopy 100, 391 (2004)

The adhesive force of FP larger than no FP region on the landing site.


Roughness and adhesion of landing sites

g g g

PFDA delaminatedfrom the interface

Formation of high energy surfaceincreases the water adsorption,

Wear could initiate if contact occurs at the

Weak bonds exist close to the from the interface increases the water adsorption,

which in turn leads to large adhesioncontact occurs at the defects sites

close to the uncovered sites

Assembledmolecules

Residualhead groups

Molecularfragments

Uncoveredsites

Defectsin PFDA

Watermolecule

Mechanisms for Wear and Stiction


The “soft” stuck micromirror (S) contains the debris at the edges


( ) g

“Soft” Stuck MicromirrorH. Liu and B. Bhushan, J. Vac. Sci. Technol. A 22, 1388 (2004)


“Soft” stuck mechanisms


H. Liu and B. Bhushan, Nanotechnology 15, 1246 (2004)

Biomimetics

Lessons From Nature (Biomimetics)Biomimetics• Nature has gone through evolution over 3.8 billion years. It has evolved

objects with high performance using commonly found materials.Biological inspired design or adaptation or deri ation from nat re is• Biological inspired design or adaptation or derivation from nature is referred to as biomimetics. It means mimicking biology or nature. Biomimetics is derived from a Greek word “biomimesis.” Other words used include bionics biomimicry and biognosisused include bionics, biomimicry and biognosis.

• Biomimetics involves taking ideas from nature and implementing them in an application.Biological materials have hierarchical structure made of commonly• Biological materials have hierarchical structure, made of commonly found materials.

100• It is estimated that the 100 largest biomimetic products had generated $1.5 billion over 2005-08. The annual sales are expected to continue to increase dramatically.


40M. Nosonovsky and B. Bhushan (2008), Multiscale Dissipative Mechanisms and Hierarchical Surfaces: Friction, Superhydrophobicity, and Biomimetics, Springer-Verlag, Heidelberg, Germany; B. Bhushan (2007), Springer Handbook of Nanotechnology, second ed., Springer-Verlag, Heidelberg, Germany; B. Bhushan, Phil. Trans. R. Soc. A 367, 1445-1486 (2009).

Montage of some examples from nature.


41B. Bhushan, Phil. Trans. R. Soc. A 367, 1445-1486 (2009).

Hiearchical Nanostructures for Superhydrophobicity, self-cleaning and low adhesion

One of the crucial property in wet i t i ttienvironments is non-wetting or

superhydrophobicity and self cleaning. These surfaces are of interest in various applications, e.g., self cleaning windows,

i d hi ld t i i t f b ildiwindshields, exterior paints for buildings, navigation-ships and utensils, roof tiles, textiles and reduction of drag in fluid flow, e. g. in micro/nanochannels. Also,

h d h bi f b d fsuperhydrophobic surface can be used for energy conservation and energy conversion such as in the development of a microscale capillary engine.

Reduction of wetting is also important in reducing meniscus formation, consequently reducing stiction.

Various natural surfaces, including various leaves, e. g. Lotus, are known to be superhydrophobic, due to high roughness and the presence of a wax coating


SEM of Lotus leaf showing bump structure. and the presence of a wax coating (Neinhuis and Barthlott, 1997)

NY Times, 1/27/05; ABCNEWS.com, 1/26/05; Z. Burton and B. Bhushan, Ultramicroscopy 106, 709 (2006); B. Bhushan and Y. C. Jung, Nanotechnology 17, 2758 (2006); B. Bhushan and Y. C. Jung, J. Phys.: Condens. Matter 20, 225010 (2008)


Rolling off liquid droplet over superhydrophobic Lotus leaf with self cleaning ability

Roughness optimization model for superhydrophobic and selfRoughness optimization model for superhydrophobic and self cleaning surfaces

Composite interfaceComplete wetting In fluid flow, another property of interest is contact angleinterest is contact angle

hysteresis (θH)

α : Tilt angle

)1cosθ(2)cosθ(cosθ1

θθθ0

adv0rec0recadvH +

−−≈−=

f

LAf

RfR

Cassie-Baxter equation: for high contact angle

Wenzel’s equation:

Droplet of liquid in contact with a smooth and rough surface

SL 0 LAcos cosfR f fθ θ= −

0 LA 0cos ( cos 1)f fR f Rθ θ= − + Increase in fLA and reduction in Rf decrease θH

for high contact angle(θ 180°)

htt //l t h i t d /th l t ff t htcos cosf oRθ θ=

M. Nosonovsky and B. Bhushan, Microsyst. Tech. 11, 535 (2005); ibid, 231 (2006); Microelectronic Eng. 84, 387 (2007); Ultramicroscopy 107, 969 (2007); Nano Letters 7, 2633 (2007); J. Phys.: Condens. Matter 20, 225009 (2008); US Patent pending (2005); Y.C. Jung and B. Bhushan, Nanotechnology 17, 4970 (2006); B. Bhushan and Y.C. Jung, J. Phys.: Condens. Matter 20, 225010 (2008)


http://lotus-shower.isunet.edu/the_lotus_effect.htm

Fabrication and characterization of nanopatterned polymers

Nanopatterns Micropatterns

Study the effect of nano- and microstructure on superhydrophobicityFabrication and characterization of nanopatterned polymers

Low aspect ratio (LAR) – 1:1 height to diameter

High aspect ratio (HAR) – 3:1 height to diameter Lotus patterned

• MaterialsSample

Poly(methyl methacrylate) (PMMA) (hydrophilic) for nanopatterns and micropatterns

Hydrophobic coating for PMMAPerfluorodecyltriethyoxysilane (PFDTES) (SAM)

Z. Burton and B. Bhushan, Nano Letters 5, 1607 (2005); Y. C. Jung and B. Bhushan, Nanotechnology 17, 4970 (2006); B. Bhushan and Y. C. Jung, J. Phys.: Condens. Matter 20, 225010 (2008);Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics

Contact angle on micro-/nanopatterned polymersContact angle on micro-/nanopatterned polymers• Different surface structures: film, Lotus, LAR, HAR• Hydrophobic film, PFDTES, on PMMA and PS surface structures

LAR HAR Lotus

Rf 2 1 5 6 3 2• In hydrophilic surfaces, contact angle decreases with roughness and in

hydrophobic surfaces, it increases.• The measured contact angles of both nanopatterned samples are higher

Rf 2.1 5.6 3.2

g p p gthan the calculated values using Wenzel equation. It suggests that nanopatterns benefit from air pocket formation. Furthermore, pining at top of nanopatterns stabilizes the droplet.


Fabrication and characterization of micropatterned silicon

Transition for Cassie-Baxter to Wenzel regime depends upon the roughness spacing and radius of droplet. It is of interest to understand the role of roughness

d di f th d l t

Fabrication and characterization of micropatterned silicon

and radius of the droplet.Optical profiler surface height maps of patterned Si with PF3

• Different surface structures with flat-top cylindrical pillars:Diameter (5 µm) and height (10 µm) pillars with different pitch valuesDiameter (5 µm) and height (10 µm) pillars with different pitch values

(7, 7.5, 10, 12.5, 25, 37.5, 45, 60, and 75 µm)

• MaterialsSample – Single-crystal silicon (Si)

Hydrophobic coating – 1, 1, -2, 2, -tetrahydroperfluorodecyltrichlorosilane (PF3) (SAM)


B. Bhushan and Y. C. Jung, Ultramicroscopy 107, 1033 (2007); J. Phys.: Condens. Matter 20, 225010 (2008); B. Bhushan, M. Nosonovsky, and Y. C. Jung, J. R. Soc. Interf. 4, 643 (2007); Y. C. Jung, and B. Bhushan, Scripta Mater. 57, 1057 (2007); J. Microsc. 229, 127 (2008); Langmuir 24, 6262 (2008); M. Nosonovsky and B. Bhushan, Ultramicroscopy 107, 969 (2007); Nano Letters 7, 2633 (2007); J. Phys.: Condens. Matter 20, 225009 (2008); Mater. Sci. Eng.:R 58, 162 (2007) ; Langmuir 24, 1525 (2008)

Cassie-Baxter to Wenzel Regime Transition criteria for gpatterned surfaces

• The curvature of a droplet is governed by Laplace eq which relates pressure• The curvature of a droplet is governed by Laplace eq. which relates pressure inside the droplet to its curvature. The maximum droop of the droplet

D)P2(δ2−

≈

Transition from Cassie-Baxter regime to Wenzel regime

• Geometry (P and H) and radius R govern transition A droplet with a large radius

If δ ≥ H

R


• Geometry (P and H) and radius R govern transition. A droplet with a large radius (R) w.r.to pitch (P) would be in Cassie-Baxter regime.

Y. C. Jung, and B. Bhushan, Scripta Mater.57, 1057(2007); Y. C. Jung, and B. Bhushan, J.Microsc. 229, 127 (2008); B. Bhushan and Y. C. Jung, J. Phys.: Condens. Matter 20, 225010 (2008)

Contact angle hysteresis and tilt angle on patterned Si surfaces with PF3Contact angle, hysteresis, and tilt angle on patterned Si surfaces with PF3

Droplet size = 1 mm in radius

• For the selected droplet, the transition occurs from Cassie-Baxter regime to Wenzel regime at higher pitch values for a given pillar height.

B. Bhushan, and Y. C. Jung, Ultramicroscopy 107, 1033 (2007); Y. C. Jung, and B. Bhushan, J. Microsc. 229, 127 (2008); B. Bhushan and Y. C. Jung, J. Phys.: Condens. Matter 20, 225010 (2008) Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics

• The critical radius of droplet for the transition increases with the pitch based on both the transition criterion and the experimental data.


Structure of ideal hierarchical surfaceStructure of ideal hierarchical surface

• Based on the modeling and observations made on leaf surfaces, hierarchical surface is needed to develop composite interface with high stability.

• Proposed transition criteria can be used to calculate geometrical parameters for a given droplet radius. For example, , for a droplet on the order of 1 mm or larger, a value of H on the order of 30 μm, D on the order of 15 μm and P on the order of 130 μm is optimum.Nanoasperities should have a small pitch to handle nanodroplets less than 1• Nanoasperities should have a small pitch to handle nanodroplets, less than 1 mm down to few nm radius. The values of h on the order of 10 nm, d on the order of 100 nm can be easily fabricated.


Fabrication and characterization of hierarchical surfaceFabrication and characterization of hierarchical surface

Fabrication of microstructure

• MicrostructureReplication of Lotus leaf and micropatterned silicon surface using


Replication of Lotus leaf and micropatterned silicon surface using an epoxy resin and then cover with the wax material

B. Bhushan et al., Soft Matter 4, 1799 (2008); Appl. Phys. Lett. 93, 093101 (2008); Ultramicroscopy (in press); Langmuir 25, 1659-1666 (2009); Koch et al., Soft Matter 5, 1386-1393 (2009)

Fabrication of nanostructure and hierarchical structureab cat o o a ost uctu e a d e a c ca st uctu e

Recrystallization of wax tubules

• NanostructureSelf assembly of the Lotus wax deposited by thermal evaporation

E pose to a sol ent in apor phase for the mobilit of a molec les


Expose to a solvent in vapor phase for the mobility of wax molecules• Hierarchical structure

Lotus and micropatterned epoxy replicas and covered with the tubules of Lotus waxB. Bhushan et al., Soft Matter 4, 1799 (2008); Appl. Phys. Lett. 93, 093101 (2008); Ultramicroscopy (in press); Langmuir 25, 1659-1666 (2009); Koch et al., Soft Matter 5, 1386-1393 (2009)

Static contact angle, contact angle hysteresis, tilt angle and adhesive force on various structures

• Nano- and hierarchical structures with tubular wax led to high static contact angle of 167º and 173º and low hysteresis angle on the order of 6º and 1º.


• Compared to a Lotus leaf, hierarchical structure showed higher static contact angle and lower contact angle hysteresis.

B. Bhushan, Y. C. Jung, A. Niemietz, and K. Koch, Langmuir (in press)

Self-cleaning efficiency of various surfaces

• As the impact pressure of the droplet is zero or low, most of particles on nanostructure were removed by water droplets, resulting from geometrical scale effects.


• As the impact pressure of the droplet is high, all particles which are sitting at the bottom of the cavities between the pillars on hierarchical structure were removed by the water droplets.

Hierarchical Nanostructures for Reversible Adhesion(Gecko Feet)

Several creatures, including insects (beetles, flies), spiders and lizards (e.g., Gecko)

• Gecko is capable of producing 20 N of adhesive force

have unique ability to cling to ceilings and walls utilizing dry adhesion. They can also detach at will by peeling.

20 N of adhesive force• This ability is due to the

hierarchical structure of the skin of the gecko.

L ll t b h• Lamellae, setae, branches, spatulae

Potential Uses of Replicated structuresCourtesy MPI Stuttgart

Potential Uses of Replicated structures• Everyday objects

Adhesive tape, fasteners, and toys• High technology applications

Nanoprobe Laboratory for Bio- & Nanotechnology and BiomimeticsGecko

Microelectronic and space applicationsTread of wall climbing robots

Hierarchical structure for adhesion enhancement

Lamellaelength 1 2 mmlength 1-2 mm

Upper level of Uppe e e osetalength 30-130 µmdiameter 5-10 µm

14000 mm-2

Brancheslength 20-30 µmdiameter 1-2 µm

ρ ~14000 mm

Spatulaelength 2-5 µmdiameter 0 1 0 2 mdiameter 0.1-0.2 µmρ/seta 100-1000

Tokay Gecko Surface Construction (Autumn et al., 2000; Gao et al., 2005; Autumn, 2006)


Simulation model

Schematic of three layer hierarchical morphology of gecko seta with three levels of branches: seta level, middle level, and spatula level. One- two- and three-level spring models for simulation


One-, two- and three-level spring models for simulation effect hierarchical morphology on interaction seta with rough surface.

B. Bhushan and R. Sayer, Applied Scanning Probe Methods VII, 41-76 (2007); Microsyst. Technol. 13, 71 (2007). B Bhushan, A. Peressadko, and T. W. Kim, J. Adhesion Sci. & Technol. 20, 1475 (2006); T. W. Kim and B. Bhushan, ibid, 21, 1 (2007); Ultramicroscopy (in press); J.Vac. Sci. Technol. A 25, 1003 (2007); J.R.Soc.Interf. (in press)

For one-level model elastic force F in the springs (k ) due to compression of :lΔFor one-level model, elastic force, Fel in the springs (kI) due to compression of :lΔ

F t l l d l1

p

el I i ii

F k l u=

= − Δ∑ 10i

if contactu

if no contact⎧

= ⎨⎩

For two-level model,10ji

if contactu

if no contact⎧

= ⎨⎩

( )1 1

q p

el ji ji j jij i

F k l l u= =

= − Δ − Δ∑∑

( )q pr

el kji kji kj j kjiF k l l l u= − Δ − Δ − Δ∑∑∑10kji

if contactu

if no contact⎧

= ⎨⎩

For three-level model,

Adhesive force between hemispherical tip of a single spatula of radii R with work

( )1 1 1

j j j j jk j i= = =∑∑∑ 0 if no contact⎩

where p, q and r are number of springs in level I, II and III of the model, respectively.

Adhesive force between hemispherical tip of a single spatula of radii Rc with work of adhesion of two surfaces Ead (DMT theory)

2ad c adF R Eπ=


Springs are pulled away from the surface when the net force (pull off force – attractive adhesive force) at the interface is equal to zero.

The effect of multi-level hierarchical structures on adhesion enhancement

0

20 Three-level Two-level One-level(μ

N)

B B' B''

A

Ead

300 Three-level (0.1kIII) Three-level (kIII ) Two-level

n co

eff.

(%)

-20

Spr

ing

forc

e

Fad

200

se o

f adh

esio

n

-6 -4 -2 0 2-60

-40

CC'C''

100

elat

ive

incr

eas

The rate of relative increase for adhesive force a between one- and multi-level models.

0

20

e (μ

N)

00 .01 0.05 0.1 0.5 1 3 5 10 30

Re

Force-distance curves of one-, two- and three-level models in contact with rough surfaces with two

force a between one and multi level models.

-40

-20

Spr

ing

forc

e


models in contact with rough surfaces with two different s values.

-6 -4 -2 0 2-60

Distance (μm)

Study of a microstructured tape y p(PVC base with nanocomposite cylindrical pillars)


Coefficient of static and kinetic friction

Based on potato beetle – insect, easier to fabricate (MPI Stuttgart)

61

Spiderman toy (about 40 g) with a hand covered with the molded polymer hairs,

clinging to a glass plate (Geim et al., 2003)


62

Summary of nanotribology of lubricants, bioadhesion and device level studies as well as hierarchical surfaces and reversible adhesion

L b i t f MEMS/NEMS• Lubricants for MEMS/NEMSBonded PFPE lubricants and SAMs appear to be the best suited for lubrication of MEMS/NEMS

• Bioadhesion studiesAdhesion between silica surfaces and biomolecules using chemical linker method isAdhesion between silica surfaces and biomolecules using chemical linker method is stronger than by direct adsorption

• Device level studiesWear of the SAMs lubricant at the defects region can lead to the increase of surface genergy which causes the increase of adhesion and lead to “hard” stiction. Micromirror sidewall contamination particles could cause micromirror “soft” stiction.A novel microtriboapparatus has been used to measure adhesion, friction and wear between MEMS components. SAMs appear to exhibit low adhesion and friction.

• Hierarchical surfacesOptimum roughness distribution can be used to generate superhydrophobic surfaces.Formation of air pockets is desirable. A transition criterion has been proposed.

• Reversible adhesion (Gecko feet)Hierarchical structure results in adhesion enhancement.


Acknowledgements

Fi i l t h b id d b th N ti l S i F d ti• Financial support has been provided by the National Science Foundation (Contract No. ECS-0301056 ), the Nanotechnology Initiative of the National Institute of Standards and Technology in conjunction with Nanotribology Research Program (Contract No. 60 NANB1D0071), and Texas Instruments, g ( ), ,Intel Corp and Nanochip Inc.

• Polysilicon and SiC work was performed in collaboration with Prof. M. Mehregany and Dr. C. A. Zorman at Case Western Reserve Universityg y y

• Some of the SAMs were prepared by Drs. P. Hoffmann and H. J. Mathieu at EPFL Lausanne, Switzerland.

• Some of the patterned samples were prepared by Dr E Y Yoon at KIST• Some of the patterned samples were prepared by Dr. E. Y. Yoon at KIST, Korea and Dr P. Hoffmann at EPFL Lausanne, Switzerland.

• The BioMEMS/BioNEMS studies were carried out in collaboration with Prof. S C Lee of OSU Medical School and Prof D Hansford of Biomedical EngS. C. Lee of OSU Medical School and Prof. D. Hansford of Biomedical Eng.

• DMD chips were supplied by Dr. S. Joshua Jacobs of Texas Instruments


References• B. Bhushan (1999), Handbook of Micro/Nanotribology, 2nd ed., CRC Press, Boca Raton, Florida.

B Bh shan (2008) Nanotribolog and Nanomechanics An Introd ction 2nd ed Springer• B. Bhushan (2008), Nanotribology and Nanomechanics – An Introduction, 2nd ed., Springer, Heidelberg.

• M. Nosonovsky and B. Bhushan (2008), Multiscale Dissipative Mechanisms and Hierarchical Surfaces: Friction, Superhydrophobicity, and Biomimetics, Springer, Heidelberg, Germany.

• B. Bhushan (2007), Springer Nanotechnology Handbook, 2nd ed., Springer, Heidelberg.B. Bhushan (2007), “Nanotribology and Nanomechanics of MEMS/NEMS and BioMEMS/BioNEMS Materials and Devices,” Microlectronic Eng. 84, 387-412.

• B. Bhushan (2008), “Nanotribology and Nanomechanics in Nano/Biotechnology,” Phil. Trans. R. Soc. A 366, 1405-1424.

• B. Bhushan (2009), “Biomimetics – Lessons from Nature: An Overview,” Phil. Trans. R. Soc. 367, 1445-1486 (2009).

• Bhushan B (2007) “Adhesion of Multi-Level Hierarchical Attachment Systems in Gecko Feet ” JBhushan, B. (2007), Adhesion of Multi Level Hierarchical Attachment Systems in Gecko Feet, J. Adhesion Sci. Technol. 21, 1213-1258.

• Bhushan, B., Y. C. Jung and K. Koch (2009), “Micro-, Nano-, and Hierarchical Structures for Superhydrophobicity, Self-Cleaning, and Low Adhesion,” Phil. Trans. R. Soc. A (in press).

H Li d B Bh h (2004) “N t ib l i l Ch t i ti f Di it l Mi i D i• H. Liu and B. Bhushan (2004), “Nanotribological Characterization of Digital Micromirror Devices using an Atomic Force Microscope,” Ultramicroscopy, 100, 391-412.

• Kasai, T., Bhushan, B., Kulik, G., Barbieri, L., and Hoffmann, P. (2005), “Nanotribological Study of Perfluorosilane SAMs for Anti-Stiction and Low Wear,” J. Vac. Sci. Technol. B 23, 995-1003.


• B. Bhushan et al., (2006), “Nanotribological characterization of perfluoroalkylphosphonateself-assembled monolayers deposited on aluminum-coatedsilicon substrates” Microsyst. Technol. 12, 588-596. http://mecheng.osu.edu/nlbb

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